This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Introduction: Preterm infants have a high incidence of metabolic acidosis. To counteract this acidosis sodium and/or potassium acetate is routinely included in total parenteral nutrition (TPN) solutions. During the first 24 to 48 hours of life neither sodium nor potassium acetate can be added to TPN fluids in premature infants. As a result, during the first few days of life, infants that develop significant metabolic acidosis are often treated with intravenous sodium bicarbonate (or volume expansion) to counteract acidosis. Both of these treatments are associated with increased morbidity and mortality. A common alternative practice is the use of a continuous sodium acetate infusion via the umbilical or peripheral arterial catheter starting on the first day of life and continuing until acetate is added to the TPN. Although this practice is widely used, no randomized control trials to investigate its efficacy have been reported. The proposed study is intended to evaluate the effectiveness and safety of a continuous sodium acetate infusion through an umbilical or peripheral arterial catheter in the first days of life to counteract early metabolic acidosis in premature infants. Research Design: This will be a prospective, randomized, double-blinded control trial, comparing arterial catheter fluids containing sodium acetate to arterial catheter fluids containing sodium chloride in premature infants less than 30 weeks gestation. Methods: Preterm neonates under 30 weeks gestation admitted to the Newborn Special Care Unit at Kapiolani (NSCU) Medical Center for Women and Children (KMCWC) and requiring either an umbilical or peripheral arterial catheter will be sequentially enrolled after obtaining informed consent. Enrolled infants will be randomly assigned to one of two study groups. The treatment group will receive 0.45% sodium acetate (0.45% NaAc) as his/her arterial catheter infusion fluid. The control group will receive 0.45% sodium chloride (0.45% NS) as his/her arterial catheter infusion fluid. Investigators and all care givers will be blinded to the type of fluid received by each infant. Data will be collected on all infants in each group during the first 5 days of life. Primary outcome measures will include serum electrolyte levels (sodium, chloride and CO2), arterial blood gas data (pH, paCO2, and base excess), use of plasma volume expansion (normal saline or albumin boluses), and sodium bicarbonate administration. A. Hypotheses: 1. The use of 0.45% NaAc arterial catheter fluids does not adversely affect serum sodium or chloride levels when compared to 0.45% NS arterial catheter fluids. 2. The use of 0.45% NaAc arterial catheter fluids significantly improves acid base status when compared to 0.45% NS arterial catheter fluids. 3. The use of 0.45% NaAc arterial catheter fluid prevents the use of volume expansion when compared to 0.45% NS arterial catheter fluids. 4. The use of 0.45% NaAc arterial catheter fluid prevents sodium bicarbonate administration when compared to 0.45% NS arterial catheter fluids. B. Objective: Determine if the use of 0.45% NaAc arterial catheter fluids results in a significant difference in serum electrolytes (sodium, chloride or CO2), acid base status and the use of volume expansion and sodium bicarbonate administration when compared to 0.45% NS arterial catheter fluids.